In a small saucepan, simmer the apple cider and maple syrup together about 20 minutes or until it reduces by half. Remove from heat and stir in half the thyme, half the marjoram and the lemon zest. Stir in the 170g butter until melted and season with salt and pepper to taste. Cover and chill in the fridge. You can make this syrup up to two days earlier.
Preheat oven to 190 degrees C. Use the lowest oven rack.
Wash and dry the turkey and place in a roasting pan. Slide your hands under the skin on the breast. Put half of the syrup under the skin. If you plan to stuff your turkey, do it now.
Spread half of the remaining syrup over the skin (reserve the last quarter of the syrup for the sauce). Truss the turkey with kitchen string.
Place the onions, celery and carrots around the turkey in the roasting pan (you can also add the neck and giblets if you wish). Sprinkle the remaining thyme and marjoram over the vegetables and add the chicken stock to the pan.
Roast the turkey 30 minutes, then reduce oven temperature to 180 degrees C and cover the turkey with foil. Cook another 3-4 hours (4-5 hours if stuffed).
Place the turkey on a serving platter and let rest 25 minutes. Meanwhile, make the gravy: pour off the liquid from the roasting pan into a small saucepan (discarding the vegetables) and skim the fat. Heat to a boil. In a bowl, combine the rest of the syrup with the flour. Whisk into the turkey juices, add the fresh thyme and bay leaf. Simmer until it thickens slightly and adjust seasoning as needed.